1. Field of the Invention
The present invention relates to a sensor control device that controls a current application state of a gas sensor element, which has at least one cell having a solid electrolyte body and a pair of electrodes, when measuring a specific gas component concentration in a gas to be measured using the gas sensor element.
2. Description of the Related Art
In the related art, a sensor control device is known that controls a current application state of a gas sensor element, which has at least one cell having a solid electrolyte body and a pair of electrodes, when measuring a specific gas component concentration in a gas to be measured using the gas sensor element.
An example of the gas sensor element is a wideband air-fuel ratio sensor provided with an oxygen pump cell and an oxygen concentration detection cell, and an example of the sensor control device is a gas sensor control device that controls the wideband air-fuel ratio sensor (see, for example JP-A-10-73564 corresponding to U.S. Pat. No. 5,976,350, FIG. 1, etc.).
Such a gas sensor control device controls a current application state of the gas sensor element so that the specific gas component concentration can be measured by heating the gas sensor element to an activation temperature using a sensor heating unit (for example, a heater) and passing a reference generation current through the oxygen concentration detection cell to thereby cause one of the pair of electrodes to function as an oxygen reference pole.
3. Problems to be Solved by the Invention
However, in the case where heating of the gas sensor element (solid electrolyte body) performed by the sensor heating unit is not sufficient (in the case where the gas sensor element is not activated), the gas sensor element may be damaged since an overvoltage may be applied to the oxygen concentration detection cell when causing a reference generation current to flow.
That is, in the case where activation of the gas sensor element is not sufficient, reaching a specified current flow through the oxygen concentration detection cell is difficult because an element impedance value of the oxygen concentration detection cell is high. Accordingly, if a preset reference generation current is caused to flow, a large voltage must be applied across the oxygen concentration detection cell. As a result, an overvoltage is applied to the oxygen concentration detection cell, and damage (for example, blackening) of the gas sensor element may occur if the overvoltage is applied for a long period of time.